Non-insulated pipelines are made up of joined piping elements such as pipes and fittings. Such pipelines can be, for example, pipes for drinking water, wastewater, storm water, oil pipelines, gas pipelines, district cooling pipes, or district heating pipes. Several of these pipelines are normally located underground or underwater (under ditch pipelines). Pipelines for industries, refineries, etc. are also joined using non-insulated pipes and fittings and are usually located above ground. Pipes and fittings are typically made of metal or plastic, and pipes of abutting piping elements are welded together or connected using rubber ring joints. The most common problems with these non-insulated pipelines located underground or above ground are leaky joints.
An estimated 90% of all leakages in modern plastic pipelines relate to the joints between pipe lengths, and between fittings and pipe lengths. In cities, the length of each pipe in the piping system is normally about 6 meters, to allow for easier piping along existing facilities. Thus, there is a pipe joint every six meters. There are also other pipe lengths, such as pipes with a length of 12, 16, or even longer pipes. The reason for leakage at pipe joints may be that the rubber ring at one end of the pipe has not been mounted, leaks in the rubber ring joint due to dirt between rubber ring and pipe, damaged rubber ring, the tip end not being sufficiently inserted into the sleeve, excess deflection in the sleeve etc. causing the leakages. Damaged mirror welds between pipes can be found. This may occur due to improper welding temperature, inadequately cleaned weld surfaces, weld surfaces not being flat, etc.
This can have major negative consequences for the affected operations, breakdowns, costs of leaking drinking water and gases, and environmental degradation in cases of leaking sewage water, oil and gas. It is therefore important to detect leakage at an early stage and to locate the fault as precisely as possible. Even a small hole in a water supply line means significant water losses. Piping leakage accounts for about 15% of the produced drinking water in Sweden, corresponding to 3.5 m3/km per day. A hole 5 mm big costs SEK 23,000 a year in case of continued leakage. Furthermore, there are additional costs to identify the leakage. There is also continuous monitoring and identification of leakage to maintain the status of the piping network and to reduce the risk of ingress of contaminated water.
Current methods for the identification and location of leakage are associated with very high costs, not least for underground pipelines. Leakage from underwater pipelines is also difficult to detect. One method of identifying leakage from underwater sewer lines is the so-called ‘seagull method’. If the population of circulating seagulls increases sharply close to a sewer line, leakage can be suspected. Other methods may be to seal the upstream end of the pipeline to see if any water emerges from the downstream end, pressure measurements, and emptying followed by visual inspection. For underground pipelines, TV inspection is a common but costly method. Pressure pipelines from pump stations can be inspected by checking the function of the pump(s) and measuring the pressure. However, it is difficult to detect minor leakages if there are pressure sensors only at the pump station and not in the piping network.
Along pipelines there are often a number of wells that should also be continuously monitored using level monitoring, for example to avoid overflow. Flux and pressure are also measured in the wells.
Thus, there is a need to find a less costly and improved monitoring system for the identification and location of leakage in non-insulated pipes.